Any guesses at breed? Hen or Roo?

I'm new to having chickens, in fact I've only had them for 3 weeks. They will be 4 weeks old in 3 days and the breed is unknown although some have suggested three of them are Red Star hybrids. I'm starting to get really paranoid and think they are all roosters. I am certain 1 is for sure.
Any feedback would be REALLY appreciated!!